Decrease in Ribosomal RNA in Candida albicans Induced by Serum Exposure

Candida albicans is an important polymorphic human pathogen. It can switch from a unicellular yeast form to germinating hypha, which may play a role in making it the successful pathogen it is. This hyphal transformation can be triggered by various extracellular stimuli, the most potent one being serum from any source. We have previously reported that Candida albicans transiently polyadenylates portions of both the large and small subunits of ribosomal RNA, shortly after serum exposure. Northern blots at the same time suggested that serum might induce a decrease in total ribosomal RNA. We have carried out a number of experiments to carefully assess this possibility and now report that serum significantly reduces ribosomal RNA in Candida albicans. Fluorometric measurements, Northern blotting and quantitative RT-PCR, have all confirmed this decrease. Timed experiments show that serum induces this decrease rapidly, as it was seen in as early as five minutes. Cell mass is not decreased as total cellular protein content remains the same and metabolic activity does not appear to slow, as assessed by XTT assay, and by the observation that cells form hyphal structures robustly. Another hyphal inducer, N-acetylglucosamine, also caused RNA decrease, but to a lesser extent. We also observed it in non-germinating yeast, such as Candida glabrata. The reason for this decrease is unknown and overall our data suggests that decrease in rRNA does not play a causal role in hyphal transformation. Rapid and significant decrease in a molecule so central to the yeast’s biology is of some importance, and further studies, such as its effect on protein metabolism, will be required to better understand its purpose.     

Compositional and immunobiological analyses of extracellular vesicles released by Candida albicans

The release of extracellular vesicles (EV) by fungal organisms is considered an alternative transport mechanism to trans‐cell wall passage of macromolecules. Previous studies have revealed the presence of EV in culture supernatants from fungal pathogens, such as Cryptococcus neoformans, Histoplasma capsulatum, Paracoccidioides brasiliensis, Sporothrix schenckii, Malassezia sympodialis and Candida albicans. Here we investigated the size, composition, kinetics of internalization by bone marrow‐derived murine macrophages (MO) and dendritic cells (DC), and the immunomodulatory activity of C. albicans EV. We also evaluated the impact of EV on fungal virulence using the Galleria mellonella larvae model. By transmission electron microscopy and dynamic light scattering, we identified two populations ranging from 50 to 100 nm and 350 to 850 nm. Two predominant seroreactive proteins (27 kDa and 37 kDa) and a group of polydispersed mannoproteins were observed in EV by immunoblotting analysis. Proteomic analysis of C. albicans EV revealed proteins related to pathogenesis, cell organization, carbohydrate and lipid metabolism, response to stress, and several other functions. The major lipids detected by thin‐layer chromatography were ergosterol, lanosterol and glucosylceramide. Short exposure of MO to EV resulted in internalization of these vesicles and production of nitric oxide, interleukin (IL)‐12, transforming growth factor‐beta (TGF‐β) and IL‐10. Similarly, EV‐treated DC produced IL‐12p40, IL‐10 and tumour necrosis factor‐alpha. In addition, EV treatment induced the up‐regulation of CD86 and major histocompatibility complex class‐II (MHC‐II). Inoculation of G. mellonella larvae with EV followed by challenge with C. albicans reduced the number of recovered viable yeasts in comparison with infected larvae control. Taken together, our results demonstrate that C. albicans EV were immunologically active and could potentially interfere with the host responses in the setting of invasive candidiasis.     

Methanogenesis produces strong 13C enrichment in stromatolites of Lagoa Salgada,Brazil: a modern analogue for Palaeo‐/Neoproterozoic stromatolites?

Holocene stromatolites characterized by unusually positive inorganic δ¹³C_PDB values (i.e. up to +16‰) are present in Lagoa Salgada, a seasonally brackish to hypersaline lagoon near Rio de Janeiro (Brazil). Such positive values cannot be explained by phototrophic fixation of CO₂ alone, and they suggest that methanogenesis was a dominating process during the growth of the stromatolites. Indeed, up to 5 mm methane was measured in the porewater. The archaeal membrane lipid archaeol showing δ¹³C values between ?15 and 0‰ suggests that archaea are present and producing methane in the modern lagoon sediment. Moreover, ¹³C‐depleted hopanoids diplopterol and 3β‐methylated C₃₂ 17β(H),21β(H)‐hopanoic acid (both ?40‰) are preserved in lagoon sediments and are most likely derived from aerobic methanotrophic bacteria thriving in the methane‐enriched water column. Loss of isotopically light methane through the water column would explain the residual ¹³C‐enriched pool of dissolved inorganic carbon from where the carbonate constituting the stromatolites precipitated. The predominance of methanogenic archaea in the lagoon is most likely a result of sulphate limitation, suppressing the activity of sulphate‐reducing bacteria under brackish conditions in a seasonally humid tropical environment. Indeed, sulphate‐reduction activity is very low in the modern sediments. In absence of an efficient carbonate‐inducing metabolic process, we propose that stromatolite formation in Lagoa Salgada was abiotically induced, while the ¹³C‐enriched organic and inorganic carbon pools are due to methanogenesis. Unusually, ¹³C‐enriched stromatolitic deposits also appear in the geological record of prolonged periods in the Palaeo‐ and Neoproterozoic. Lagoa Salgada represents a possible modern analogue to conditions that may have been widespread in the Proterozoic, at times when low sulphate concentrations in sea water allowed methanogens to prevail over sulphate‐reducing bacteria.     

Genomic signatures of geographic isolation and natural selection in coral reef fishes

The drivers of speciation remain among the most controversial topics in evolutionary biology. Initially, Darwin emphasized natural selection as a primary mechanism of speciation, but the architects of the modern synthesis largely abandoned that view in favour of divergence by geographic isolation. The balance between selection and isolation is still at the forefront of the evolutionary debate, especially for the world's tropical oceans where biodiversity is high, but isolating barriers are few. Here, we identify the drivers of speciation in Pacific reef fishes of the genus Acanthurus by comparative genome scans of two peripheral populations that split from a large Central‐West Pacific lineage at roughly the same time. Mitochondrial sequences indicate that populations in the Hawaiian Archipelago and the Marquesas Islands became isolated approximately 0.5 Ma. The Hawaiian lineage is morphologically indistinguishable from the widespread Pacific form, but the Marquesan form is recognized as a distinct species that occupies an unusual tropical ecosystem characterized by upwelling, turbidity, temperature fluctuations, algal blooms and little coral cover. An analysis of 3737 SNPs reveals a strong signal of selection at the Marquesas, with 59 loci under disruptive selection including an opsin Rh2 locus. While both the Hawaiian and Marquesan populations indicate signals of drift, the former shows a weak signal of selection that is comparable with populations in the Central‐West Pacific. This contrast between closely related lineages reveals one population diverging due primarily to geographic isolation and genetic drift, and the other achieving taxonomic species status under the influence of selection.     

Local knowledge and exploitation of the avian fauna by a rural community in the semi-arid zone of northeastern Brazil

Background

The present study examined the exploitation of bird species by the residents of a rural community in the Brazilian semi-arid zone, and their preferences for species with different characteristics.

Methods

The 24 informants were identified using the “snowball” approach, and were interviewed using semi-structured questionnaires and check-sheets for the collection of data on their relationship with the bird species that occur in the region. The characteristics that most attract the attention of the interviewees were the song and the coloration of the plumage of a bird, as well as its body size, which determines its potential as a game species, given that hunting is an important activity in the region.

Results

A total of 98 species representing 32 families (50.7% of the species known to occur in the region) were reported during interviews, being used for meat, pets, and medicinal purposes. Three species were used as zootherapeutics – White-naped Jay was eaten whole as a cure for speech problems, the feathers of Yellow-legged Tinamou were used for snakebite, Smooth-billed Ani was eaten for “chronic cough” and Small-billed Tinamou and Tataupa Tinamou used for locomotion problems. The preference of the informants for characteristics such as birdsong and colorful plumage was a significant determinant of their preference for the species exploited. Birds with cynegetic potential and high use values were also among the most preferred species. Despite the highly significant preferences for certain species, some birds, such as those of the families Trochilidae, Thamnophilidae, and Tyrannidae are hunted randomly, independently of their attributes.

Conclusion

The evidence collected on the criteria applied by local specialists for the exploitation of the bird fauna permitted the identification of the species that suffer hunting pressure, providing guidelines for the development of conservation and management strategies that will guarantee the long-term survival of the populations of these bird species in the region.

     

Deciphering unusual uncultured magnetotactic multicellular prokaryotes through genomics

Candidatus Magnetoglobus multicellularis (Ca. M. multicellularis) is a member of a group of uncultured magnetotactic prokaryotes that possesses a unique multicellular morphology. To better understand this organism''s physiology, we used a genomic approach through pyrosequencing. Genomic data analysis corroborates previous structural studies and reveals the proteins that are likely involved in multicellular morphogenesis of this microorganism. Interestingly, some detected protein sequences that might be involved in cell adhesion are homologues to phylogenetically unrelated filamentous multicellular bacteria proteins, suggesting their contribution in the early development of multicellular organization in Bacteria. Genes related to the behavior of Ca. M. multicellularis (chemo-, photo- and magnetotaxis) and its metabolic capabilities were analyzed. On the basis of the genomic–physiologic information, enrichment media were tested. One medium supported chemoorganoheterotrophic growth of Ca. M. multicellularis and allowed the microorganisms to maintain their multicellular morphology and cell cycle, confirming for the first time that the entire life cycle of the MMP occurs in a multicellular form. Because Ca. M. multicellularis has a unique multicellular life style, its cultivation is an important achievement for further studies regarding the multicellular evolution in prokaryotes.